1. Field of the Invention
The present invention relates to encapsulation compositions in which an encapsulate is encapsulated in a glassy matrix by a process known as melt extrusion. More particularly, the present invention relates to flavor encapsulation compositions in which a flavoring agent is encapsulated by melt extrusion in a glassy matrix containing spices and herbs as a part of the matrix. Incorporation of spices and herbs in the matrix creates an active carrier protecting and modulating the encapsulated flavoring agents. The present invention also relates to processes for preparing such compositions.
2. Discussion of the Background
The encapsulation of encapsulates is an area of active research. In particular, the encapsulation of encapsulates such as medications, pesticides (including insecticides, nematocides, herbicides, fungicides, microbiocides, etc.), preservatives, vitamins and flavoring agents is desired for a number of reasons. In the case of medications and pesticides, encapsulation may be desired to achieve controlled release of the medications or the pesticides. For vitamins, encapsulation may be carried out to protect the vitamins from air-oxidation and, thus, to extend shelf life of the vitamins. In the case of flavoring agents, the encapsulation may be carried out to place the flavorings in an easily metered form which will release the agent at a controllable event, such as the addition of water.
It is generally known to skilled practitioners in the field of flavor encapsulation that the current practical commercial processes leading to stable, dry flavors are limited in great part to spray drying and extrusion fixation. The former process requires emulsification or solubilization of the flavor in an aqueous carrier containing the encapsulation solids, followed by rapid drying in a high temperature, high velocity gas stream and collection as a low-density bulk solid.
While spray drying accounts for the majority of commercially encapsulated flavor materials, several limitations of the process are evident. Low molecular weight components of complex or natural flavor mixtures generally exhibit high vapor pressures and are usually lost or disproportionate during the process. The resultant flavor-carriers are porous and difficult to handle. In addition, deleterious chemical reactions such as oxidation can result on surfaces exposed during and after drying. The final product, a dry, free flowing fine powder will release the encapsulate rapidly upon hydration whether rapid release is desired or not. Incorporation of spices or herbs in a significant amount in the solubilized carrier is not practical for the reason of swelling of a spice or an herb powder in water, resulting in a high viscosity and clogging atomizing wheels or nozzles during spray drying.
Some other encapsulation processes may include freeze drying, drum drying and tray drying. These processes have marginal significance due to a high processing cost and relatively poor protection of encapsulates, compared to spray drying and extrusion. The processes of drying are slow in the case of freeze and tray drying resulting in a weak glassy character generated by slow drying rather than quick cooling. Volatile flavor losses are very significant. Drum drying could be a fast process; however, loss of volatile components is very significant on the contact with a high temperature surface. All the above processes require a milling step further weakening the flavor. Moreover, the preparation step involves making a slurry where spices and herbs will swell and form a viscous dispersion that is difficult to control and process.
U.S. Pat. No. 3,971,852 discloses the use of a modified starch, gums and other food polymers with low molecular weight polyhydroxy compounds and spray drying to yield a glassy matrix with encapsulated oil at a maximum of 70-80% by volume. The system forms a shell surrounding the oil flavoring but is limited to lipophilic flavoring agents.
U.S. Pat. No. 4,532,145 discloses a process for preparing compositions in which a volatile flavorant is fixed by spray drying from a carrier solution made up of 10-30% of a low molecular weight component such as a sugar or edible food acid with the balance of the solids being a maltodextrin carbohydrate in the amount of 70-90%.
U.S. Pat. No. 5,124,162 discloses a carrier mixture composed of mono- and disaccharides (22-45%), maltodextrins (25-50%), and a high molecular weight carbohydrate such as chemically modified starch or gum acacia (10-35%) to which volatile flavoring agents are added and the subsequent dispersion is spray dried to yield a free flowing powder with a bulk density of 0.50 g/cc.
A number of technical issues are unmet by these approaches. First, thermally sensitive flavors undergo undesirable reactions including oxidation, rearrangements, and hydrolysis. Secondly, volatile components are lost or disproportionate during atomization and evaporation in the dryer. Finally, spices and herbs are not included in the compositions.
A second process route, melt injection, has been utilized to advantage with lipid-based flavors. In this technology, a melt is prepared by boiling off sufficient water from a high solids carbohydrate syrup, adding flavoring oils with an emulsifier, agitating under pressure to emulsify the oil in the melt and injecting the mixture into a chilling, dehydrating solvent bath to obtain fine rod-like filaments. After solvent removal, the matrix is reduced in size and, in some cases, coated with an anti-caking agent before being packed. See, e.g., U.S. Pat. Nos. 2,809,895; 2,856,291; and 3,704,137. Subsequent improvements in the art are disclosed in U.S. Pat. No. 3,314,803 for the encapsulation of volatiles such as acetaldehyde, and in U.S. Pat. No. 4,707,367, which discloses encapsulation of up to 35% by weight of flavor oil in the glassy matrix.
U.S. Pat. No. 4,689,235 discloses the use of modified starch-maltodextrin carriers in the range of 5 parts modified starch/95 parts maltodextrin to 95 parts modified starch/5 parts maltodextrin. The carrier is dissolved to form a syrup, water is cooked off, flavor is added and emulsified, and the melt is injected into a solvent bath.
An alternative route to encapsulating flavors is disclosed in U.S. Pat. No. 4,230,687. In this approach, high molecular weight carriers such as proteins, starches and gums are plasticized by addition of significant amounts of water in the presence of the encapsulate and subjected to a high shear dispersing process. The rubbery or plastic matrix with encapsulate is then extruded, recovered and dried to yield a stable product.
Another alternative process, melt extrusion, can be utilized for flavor fixation and encapsulation. In this process, a melting system, i.e., an extruder is employed to form the carrier melt in a continuous process. The encapsulated flavor is either admixed or injected into the molten carbohydrate carrier.
U.S. Pat. No. 4,232,047 discloses the use of a matrix comprising a fused encapsulating material selected from the group consisting of starches, cereal flour, modified starches, gums, proteins, and mixtures thereof to encapsulate essential oils, oleoresins, and mixtures. The composition is melted in the presence of 10% to 40% by weight of water and extruded under non-puffing conditions. The flavor agent forms a micro dispersion in the glasseous melt.
U.S. Pat. No. 5,972,395 discloses the use of a matrix composed of 15 to 40% of a high molecular weight carrier, preferably a maltodextrin and at least 40% of a low molecular weight carbohydrate, sugar polyol, or adipic acid. The matrix is extruded to yield a solid matrix characterized as a glass.
U.S. Pat. Nos. 5,087,461 and 5,009,900 disclose utilizing a composition consisting of a modified food starch, maltodextrin, polyol, and mono- and disaccharide components. The starch is a chemically-modified water-soluble starch and is used in the amount of 40 to 80% of the total mixture. The balance of the composition is comprised of 10 to 40% maltodextrin, 5 to 20% corn syrup solids or polydextrose, and 5 to 20% mono- or disaccharide. This matrix is said to balance processing response with glass matrix character.
U.S. Pat. No. 5,756,136 discloses the encapsulation of cinnamic aldehyde in a matrix containing at least 25% of a whey protein isolate. The resulting encapsulate exhibits a control release functionality and protection for yeast-leavened dough.
U.S. Pat. Nos. 6,652,895; 6,416,799; 6,187,351; 5,603,971; and 5,897,897 disclose the use of a series of extrusion matrix compositions. The use of water to plasticize the matrix in the extrusion process yields an encapsulated flavor matrix characterized by glass transition temperatures greater than 40° C. In U.S. Pat. No. 6,652,895, a composition containing a carboxylate or sulfate containing food polymer and the presence of calcium ions in the melt is disclosed. In U.S. Pat. No. 6,416,799, a composition containing a maltodextrin with buffering organic acid-acid salts is disclosed. In U.S. Pat. No. 6,187,351, a composition containing 2 to 45% of a food polymer, 25 to 80% of a maltodextrin, and 10 to 30% of a mono- or disaccharide or 24 D.E. to 42 D.E. corn syrup solids is disclosed. The matrix is dry blended, fed into the extruder with the required water plasticizer and flavor, and the resulting encapsulate is obtained as a glassy solid exhibiting a glass transition temperature greater than 40° C. The disclosed polymers include modified celluloses, high methoxy pectin, gum arabic (acacia), locust bean gum, guar gum, and lesser gums such as gum ghatti, gum tragacanth and gum karaya. Also disclosed are proteins such as gelatin and casein, microbial gums such as xanthan and gellan, pregelatinized starches in addition to other carbohydrate polymers such as inulins, beta-glucans and konjac flour.
U.S. Patent Application 2002/0189493 discloses the use of majority, single polymer component compositions with melt extrusion encapsulation. In one case, a matrix composed of a binary polymer composition selected from the group of gelatin, hydrolyzed gelatin, larch gum and gum arabic at 0 to 50% of the individual polymers is disclosed.
U.S. Patent Application 2002/0187223 teaches the use of prehydrated agar agar (at 1-7% levels) with other carriers which are mixed with a flavor, extruded and dried to form a glassy matrix encapsulating media.
U.S. Pat. No. 4,816,298 discloses the preparation of a cold-water dispersible granular composition comprising a plasticizer and thermally moldable polymers. The polymers are selected from the group of methyl cellulose, hydroxypropyl methylcellulose, carboxymethyl cellulose, and hydroxypropyl cellulose and are extruded at an elevated temperature with plasticizer to yield a cold-water dispersible matrix.
In a number of the cited patents which disclose melt extrusion, the matrix compositions were carefully defined to accommodate processing limitations of the extruder, as well as to generate a stable matrix in the glassy state characterized by a glass transition temperature of greater than 40° C. The cited patents describe liquid flavor, essential oils, oleoresins, processed flavors, medications, pesticides, and vitamins as encapsulates.
Formation of a matrix in the glassy state is of particular value for encapsulation of water-soluble flavorings and extracts. The role of water as a plasticizing agent conflicts with the desired results, because water has the effect of lowering the glass transition temperature (Tg) of the glassy matrix. In model studies of a number of food carbohydrate systems, the upper limit of water content is approximately 7 to 10 wt. % for lower molecular weight components such as mono- and disaccharides, maltodextrins, food polymers and combinations of these agents. At higher water contents, the Tg is lowered to the extent that the matrix is in the undesirable rubbery, plastic or fluid state at room temperatures.
In order to insure a higher Tg, several options are available. By limiting the class of encapsulate materials to lipophilic materials such as citrus oils, plasticizing moisture can be removed by a boil off process as described in U.S. Pat. Nos. 2,856,291; 2,809,895; 3,314,803; 3,704,137; and 4,707,367. Alternatively, the use of melt injection limits the flavoring agents to materials with lower vapor pressure which can be admixed to the composition before melting. Flavorings which are in the form of aqueous extracts, water, or alcohol-water solutions will result in a product with a Tg much below 25° C. leading to plastic flow and loss of volatiles upon storage.
Similarly, in U.S. Pat. Nos. 5,009,900 and 5,972,395, the flavorings are limited to those with limited volatility, and total moisture level in the product is less than 11% by weight. Many of the key top notes and unique flavor components of complex flavors have high vapor pressures at room temperature and are not easily encapsulated by such a process.
Matrix improvements for the continuous melt extrusion process are described in U.S. Pat. Nos. 6,652,895; 6,416,799; 6,187,351; 5,603,971; and 5,897,897. The use of modified starch and food polymers with low molecular weight carbohydrate plasticizers is detailed to yield encapsulates in a glassy matrix with a Tg greater than 40° C. However, with these matrices, the flavor loads are generally limited to 10 wt. % or less. Encapsulates described were medications, pesticides, vitamins, preservatives, and flavoring agents, wherein the flavoring agent is selected from the group consisting of natural extracts, oleoresins, essential oils, protein hydrolyzates, aqueous reaction flavors, compounded natural flavors, and artificial flavors.
Preparation of a solid in the glassy state is dependent upon both matrix composition and the process used to generate the encapsulating material. The advantages of retaining the glass form of the matrix include increased physical stability of the solid, reduced loss of incorporated volatiles, and reduction of deleterious intermolecular reactions and oxidation. A detailed discussion of the physical chemistry of water-food polymer interactions relating to the glassy state can be found in H. Levine and L. Slade, “Glass Transitions in Foods,” in Physical Chemistry of Foods, H. Schwartzberg and R. Hartel, Eds., Marciel Dekker, New York, pp. 83-205, 1992; and in H. Levine and L. Slade, “Water as a Plasticizer: physico-chemical aspects of low-moisture polymeric systems,” in Water Science Reviews, vol. 3, F. Franks, Ed. Cambridge University Press, London, pp. 79-185, 1988, which are incorporated herein by reference. The role of water as a plasticizer with food polymers, as well as the relationships between molecular compositions and dynamics of interactions between various components, are discussed in these references.
It is important to mention that melt extrusion is not a drying process. It generates glassy compositions by melting matrix components, followed by a quick cooling of the melt. Optionally, in-process or post-processing drying could be applied to further control moisture and other properties of the compositions. However, drying is not essential for the formation of glassy encapsulation compositions. Water or aqueous solutions used as a plasticizer are added in the amounts not preventing formation of a glassy matrix with the glass transition temperature above ambient temperature. In other words, quick cooling of the matrix makes it glassy without significant water evaporation. This distinguishes the melt extrusion process from spray-, drum-, or tray drying where a glassy matrix may be obtained mainly though evaporation of water from a slurry.
Spices and herbs in their original and ground powdered form possess unique flavor properties. More recently it has been recognized that spices and herbs contain potent antioxidants that may have protective properties for oils and flavors. The same antioxidants may be health beneficial. Thus, there remains a need for encapsulation compositions in which an encapsulate is encapsulated in an active carrier which is stable in the glassy state at ambient or slightly elevated temperatures and contains a significant amount of spices and herbs in addition to liquid or solid encapsulates. These active carriers can exhibit unique flavor interactions with encapsulates and modulate a flavor imparted by encapsulates. In turn, flavors may modulate flavor characteristics imparted by the active carrier and have an effect on bioavailability or other antioxidant or protective functions of spices and herbs. There is also a need to mask, modify or mitigate some of the intense background notes introduced by either spices, herbs or encapsulates. The glassy carriers can preserve, modulate and control release of encapsulates. There is also a need to preserve labile and sensitive flavors with natural antioxidants introduced by spices and herbs constituting a significant part of the active carrier.